The author has developed a non-intrusive spectral projection (NISP) stochastic finite element method (NISP-SFEM) that incorporates a NISP method as part of the intrusive spectral stochastic finite element method (intrusive SSFEM), and has analyzed elasto-plastic problems in the range of small strain deformations. NISP-SFEM is a hybrid method that uses the NISP method to calculate the element stiffness matrix and internal force matrix, and uses an intrusive SSFEM to solve the global stiffness matrix.
In this paper, NISP-SFEM is extended to be applicable to the problem of quasi-static finite deformation. Then the expanded NISP-SFEM is used to solve simple tension problems in which displacement is applied gradually to both sides of an elasto-plastic body with yield stress that varies stochastically. By examining the stochastic variation of the internal force-nominal strain curve, it is observed whether the stochastic variation of the stress in the stable or unstable region is accurately tracked. Furthermore, the numerical verification of NISP-SFEM is performed through comparison with the Monte Carlo method.
The data-driven approach has become a major scheme in the field of civil engineering, but as the properties of a computation model it is also required interpretability in computation process and integration with prior knowledge on natural phenomena. This research focuses on a methodology of Koopman operator analysis as a scheme of integrated data-driven and model-driven approach, and shows its effectiveness through numerical experiments. Further, the methodology is applied to a problem of short-time precipitation forecast. Considering a transient characteristic of rainfall distribution, a novel method to decompose its dynamic behavior into global advection and spatial mode is proposed and verified.
This paper proposes a method for simulating meso-scale fracture behavior of concrete with interfacial weakness using a damage model. An outstanding feature of the damage model is the ability to analyze the crack propagation in heterogeneous materials with interfacial weakness by using the volume fraction of each material in finite element that does not conform to material interfaces. Several numerical examples are presented to demonstrate the validity and availability of the proposed method. First, the formulation of the damage model is verified in one-dimensional problem. The applicability of the method to image-based analysis of concrete’s meso-structure is then demonstrated in two-dimensional beam problem. Finally, the comparison between numerical and experimental results in three-point bend test of concrete beam reveals that the proposed method allows us to simulate the three-dimensional meso-scale fracture behavior of concrete in agreement with that observed experimentally.
Repair methods for the fatigue crack in steel bridges depend on the size of the damage. Therefore, in order to perform the appropriate repair for fatigue damage, it is important to know the crack depth.
In this study, we investigated a method to estimate the crack depth for semi-elliptical surface crack based on the stress intensity factor. First, we conducted a numerical analysis to verify a method to estimate the stress intensity factor for semi-elliptical surface crack and the crack depth. From the numerical analysis results, it was shown that the crack depth could be estimated within an error of ±15%. Secondly, in order to verify the effectiveness of the proposed method, fatigue tests were conducted using tensile specimens. From those fatigue test results, the crack depth could be estimated using the estimated stress intensity factor within an error of ±28%. In addition, we examined the index to evaluate the pasting accuracy of the gauge from the measured strain data.
A Region-wise ZIG-ZAG theory that combines the improved ZIG-ZAG theory and the layer-wise theory is proposed. In this theory, the laminated structure is divided into several regions in the thickness direction, and the region boundary and inside of the region are given degrees of freedom. The high-order improved ZIG-ZAG theory is used to represent the ZIG-ZAG displacement inside the region. As a result, it is easy to apply to delamination analysis and to structures composed of composite and isotropic materials, and the number of unknown degrees of freedom is considerably smaller than the layer-wise theory. The accuracy and applicability of this theory are verified using numerical examples of bending analysis of anisotropic laminated and sandwich plates.
The effectiveness of the threshold line (TL) proposed as the criterion for setting of the opening size between the shear boxes of direct shear test based on the results of several kinds of sandy soil samples in the past study was examined by the discrete element method (DEM). The conditions of the direct shear test in the DEM simulation were reproduced using four kinds of specimens with different mean particle sizes (D50) and particle size distributions, and the shearing processes were performed according to the predetermined opening size between shear boxes. As a result, it was confirmed that the maximum difference of the threshold point (T.P) obtained by the DEM simulation was about 0.17 mm compared to the TL, and it showed almost the same trend as the TL obtained from the experiments using the real soil material. Based on the results of this study and the past study results, it can be said that the TL is not affected by the mean particle size and particle size distribution of the soil sample, and could be considered to be an effective criterion for setting of the opening size between the shear boxes of direct shear test.